1. Field of the Invention
The subject invention is directed to fuel injection nozzles for gas turbine engines, and more particularly, to a system and method for assembling components of fuel nozzles.
2. Background of the Related Art
Staged fuel injectors for gas turbine engines are well know in the art. They typically include a pilot fuel atomizer for use during engine ignition and low power engine operation and at least one main fuel atomizer for use during high power engine operation in concert with the pilot fuel atomizer. One difficulty associated with operating a staged fuel injector is that when the pilot fuel circuit is operating alone during low power operation, stagnant fuel located within the main fuel circuit can be susceptible to carbon formation or coking due to the temperatures associated with the operating environment. This can degrade engine performance over time.
In the past, attempts were made to passively insulate or otherwise protect the main fuel circuit of a staged fuel injector from carbon formation during low power engine operation using heat shields or vents. Efforts have also been made to actively cool a staged fuel injector using fuel flow from the pilot fuel circuit. One such effort is disclosed in U.S. Pat. No. 5,570,580 to Mains, which provides a fuel injector having two dual orifice injector tips, each with a primary and secondary pressure atomizer. There, fuel streams to the primary and secondary sprays of the secondary and main nozzle tips are arranged to transfer heat therebetween.
U.S. Patent Application Publication No. 2007/0163263 to Thomson, which is incorporated by reference herein in its entirety, describes an advance in the art of protecting the main fuel circuit of a staged fuel injector from carbon formation. A staged fuel injector includes a main fuel circuit for delivering fuel to a main fuel atomizer and a pilot fuel circuit for delivering fuel to a pilot fuel atomizer located radially inward of the main fuel atomizer. The pilot fuel circuit is in close proximity to the main fuel circuit en route to the pilot fuel atomizer so that the pilot fuel flow cools stagnant fuel located within the main fuel circuit during low engine power operation to prevent coking.
Conventional construction of such fuel injectors, nozzles, and atomizers includes components bonded together by braze. The components have milled slots or drilled holes to control the flow of fuel and prepare the fuel for atomization. The components are typically nested within one another and form a narrow diametral gap which is filled with a braze alloy. The braze alloy is applied as a braze paste, wire ring, or as a thin sheet shim on the external surfaces or within pockets inside the assembly. The assembly is then heated and the braze alloy melts and flows into the narrow diametral gap and securely bonds the components together upon cooling.
Such conventional methods and systems generally have been considered satisfactory for their intended purpose. However, when using traditional brazing techniques, the braze alloy must flow from a ring or pocket to the braze area. In doing so, it is prone to flow imprecisely when melted. It is also not uncommon for braze fillets to be formed on or in certain features. In some instances intricate or narrow passages can become plugged if too much braze is used. These fillets and plugs can negatively affect nozzle performance. Moreover, braze may not flow to the desired braze area in the quantity needed to ensure a proper braze joint. This is typical when the braze alloy cannot be located in close proximity to the desired braze joint location.
The difficulty in controlling braze flow employing traditional brazing techniques is a limiting factor in the design of fuel and air flow passages within a nozzle. That is, the shape and size of the flow passages is limited by the ability to control the flow of braze.
There remains a need in the art for a method and system of assembling nozzles by brazing that will eliminate or greatly reduce fillet formation and/or plugging and allow for formation of intricate internal fuel and air flow passages. There also remains a need in the art for such a method and system that are easy and inexpensive to make and use. The present invention provides a solution for these problems.